1. Field of the Invention
This invention relates to an improved method and apparatus for monitoring the performance of electromechanical systems driven by electric motors, and more particularly, relates to the measuring of friction associated with said systems.
2. Description of Prior Art
The use of motors for driving electromechanical systems, such as machines for transporting load or weight, paper feed devices, etc. are well known in the prior art. Generally the motors are servocontrolled so that precise motion is transmitted to the load. The input energy to the motor should be of a sufficient magnitude which will overcome the frictional force associated with the system, and at the same time, perform useful work such as transporting a load. Knowing the frictional force associated with a particular system will enable the optimization of power needed to drive a particular system to overcome the frictional force.
The frictional force associated with a system can be used to predict impendent failure mode in the system. For example, if the bearings in a system are beginning to wear, then by monitoring the change in the friction, one can change the bearing prior to a complete breakdown of the system.
In view of the above, there is a clear need for a device which is able to accurately measure the friction associated with a motor and/or electromechanical system. Moreover, the measuring device should be able to measure friction dynamically. As such, as the frictional characteristics of a system change due to age, worn parts, etc., the calculated value will be more accurate. The calculated value can be used for antifriction compensation or for maintaining reliability, serviceability and availability (RAS) for the system.
The effect of friction on an electromechanical system is exemplified in U.S. Pat. No. 3,916,279. In that system a controlled motor is used for lifting a load coupled through a pulley onto the shaft of the motor. A friction-simulating circuit generates a signal which compensates for the friction associated with the system. The design of the simulating circuit is based on a statistical prediction of the friction. Any deviation from the predicted value reduces the effectiveness of the circuit.